Typically, initiators used to initiate ignition of the propellant that inflates an air bag or actuates a seatbelt pretensioner of an automotive passenger restraint system comprise an electroexplosive. Such initiators generally consist of a bridgewire such as nichrome or evanhom wire that is in direct contact with an ignition composition. Ignition compositions suitable for use as initiating charges include boron-potassium nitrate and smokeless powder as taught in U.S. Pat. No. 3,715,131. The bridgewire is connected between two electrical contacts which are connected to a firing circuit. When firing current is applied to the firing circuit, the bridgewire is electrically heated, and the ignition composition is ignited. The combustion of the initiator ignites a booster charge that effects ignition of the propellant.
However, known initiators exhibit a problem in that intimate contact between the bridgewire and the ignition composition is not always assured. In addition, the hermetic seal used to protect the ignition composition often deteriorates over the lifespan of the initiator in the field. Furthermore, fabrication of known initiators is complex and costly.